A system 100 for verifying radiation dose delivered to a subject 5, comprises a portal dose imaging device 30 configured to generate portal dose images of radiation dose delivered to a subject from predetermined radiation fields； and a processing device 50 operably connected to the portal dose imaging device and configured to store the portal dose images in a first data array having spatial and angular locations of the delivered beams (X, Y, θ) as dimensions, and to store corresponding predicted portal dose images in a second data array having spatial and angular locations of the predicted beams (X, Y, θ) as dimensions； wherein the processing device compares points in the first data array with corresponding points in the second data array using a gamma evaluation method, the gamma evaluation method including dose differences, spatial differences, and angular differences between corresponding points in the first and second data arrays as parameters, and wherein the processing device determines errors in the delivered radiation dose based on the comparison
